<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <button>点击</button>
  <script>
    const btn = document.querySelector('button')
    // btn.onclick = function () {
    //   alert(11)
    // }
    // btn.onclick = function () {
    //   alert(22)
    // }

    // let num = 10
    // num = 20
    btn.addEventListener('click', function () {
      alert(11)
    })
    btn.addEventListener('click', function () {
      alert(22)
    })
  </script>
</body>

</html>